Seal structure for underground liquid storage facility



April 25, 1961 SEELY, JR 2,981,070

SEAL STRUCTURE FOR UNDERGROUND LIQUID STORAGE FACILITY Filed Aug. 31,1955 2 Sheets-Sheet 1 INVENTOR. DWIGHT H. SEELY, JR.

BY 2 ATTgRN EY April 25, 1961 D. H. SEELY, JR 2,981,070

SEAL STRUCTURE FOR UNDERGROUND LIQUID STORAGE FACILITY Filed Aug. 51,1955 2 Sheets-Sheet 2 INVENTOR. DWIGHT H.

Y ffpELY JR.

ATTO NEY United States Patent SEAL STRUCTURE FOR UNDERGROUND LIQUIDSTORAGE FACILITY Dwight H. Seely, J12, Oklahoma City, Okla, assignor toSohio Petroleum Company, Cleveland, Ohio, a corporation of Ohio FiledAug. 31, 1955, Set. o. 531,689

3 Claims. 01. 61.5)

The present invention relates to new and useful improvements inunderground storage facilities. Particularly, it relates to improvedsealing means for underground facilities used for the storage of liquidsor gases under pressure.

Recent developments in the design and construction of storage facilitieshave led to extensive use of underground facilities for the storage offluid products produced in the petroleum, chemical and petrochemicalindustries. It has been determined that underground facilitiessubstantially reduce the amount of capital required heretofore toprovide aboveground storage facilities. Underground facilities forstorage of liquids or gases under pressure have been constructed in manyplaces in this country. Generally, such facilities are of one or twotypes, the first type involving storage in underground salt domes andthe second involving mined underground caverns. My invention relatesparticularly to improvements in the construction of undergroundfacilities of the latter type.

In choosing a suitable underground stratum for the construction of amined cavern, it is customary to drill one or more cores by conventionalcore drilling methods in the general location where the facility is tobe installed. The cores obtained by such drilling make it possible toselect a geological formation having the properphysical characteristicsand located at the proper depth underground to serve as a storagecavern.

Of first consideration is the depth of the excavation to be used andthis is determined by the geological information available concerningtheability of the overburden to retain pressure. For example, for apressure of 100 pounds (gauge) an excavation or storage cavity should belocated at least 100 feet belowgro-und according to a rule isimpermeable, hard, and substantially free of fractures,

andfone having sufficient beam strength to support the necessaryoverburden. .An example of a suitable formation for a roof structurewould be massive limestone.

Of equal importance are the properties required for the walls of theexcavation. The walls of the excavation should preferably beimpermeable, reasonably dry and.

devoid of impurities or properties which might have a deleterious effectupon'the liquid stored. A suitable formation for the cavern walls wouldbe tight, sandy, shale to shaly sandstone and silty grey shale. Thisformation is dry, non-waterbearing, tight, andwill not effect the storedmaterials. If such a formation is not available, a water-bearingformation may be'employed as the stored material will displace thewater.

It is desirable, although not necessary, that the cavern formation befollowed immediately below by a hard formation suitable for acavern'floor, such, for example, as

hard brittle limestone. However, if the walls of the cavitypossess thedesired properties, a special'floor formation per se, is not required.

The foregoing information is generally known in the industries wheresuch underground caverns have been employed as storage facilities.Underground caverns are usually constructed by conventional miningmethods, e.g., a mine shaft may be first sunk to the desired depth andthe cavern is then excavated.

The particular problem I have overcome is concerned with the sealing ofthe mine shaft with respect to the cavern. The object of my invention isto provide an impermeable seal between the mine shaft and the oavern toeffectively preclude the escape of any of the material which is to bestored in the cavern.

Seals of the type contemplated herein may be disposed in any relativeposition, e.g., either vertical or horizontal. When it is desired toform one or more caverns by means of a common mine shaft, tunnels may beexcavated in several directions from the mine shaft and a cavern maythen be excavated at the terminus of each tunnel. In such a case, itwill usually be more convenient to looate the seal structure in thetunnels extending from the mine shaft. Merely for the purposes ofdescription, such a case is contemplated herein below.

There are several known methods by which such a tunnel could be sealed.For example, the tunnel leading from the cavern to the mine shaft may be.filled and sealed with concrete or cement. Alternatively the tunnelcould be sealed by means of an impervious plate embedded in the walls ofthe tunnel. In the underground storage of liquids at atmospheric or nearatmospheric pressures, such methods have generally been found to besuitable. However, when liquids or gases are stored at superatmosphericpressure, such sealing methods are not wholly effective and loseutility. For example, in the case of the underground storage ofliquefied petroleum gas, it has been found that cement is relativelyporous to such a liquid and that a dangerous amount of the liquid willescape through the concrete no matter how thick it may be, creating aconsiderable safety hazard. Since underground caverns are generallylocated in shale formations and it is a characteristic of shale that ithas a low shearing strength, the use of an impervious plate in such atunnel is not considered a satisfactory solution to the problem.

If an impervious plate is employed, such as a metal plate embedded inthe tunnel walls, there is considerabledanger of a breaking away of thetunnel wall with consequent collapse of the seal. The tunnels arefrequently ten feet or larger in diameter and consequently a metal plateinserted in the Wall to seal the tunnel imposes a substantial shearingstress on the walls of the tunnel at pressures substantially aboveatmospheric pressure. Another drawback of this type of seal is that thestored ma- I terial has a tendency to escape around the perimeter of theplate.

I have now invented a seal structure for underground storage facilitieswhich efiectively overcomes the defects inherent in the sealing means ofthe prior art. 7

In brief, the seal structure of my invention comprises an imperviousmass embedded in the Walls of the section V to be sealed having across-sectional area greater than the area of that section. Thestructure may also have provision for access therethrough.

As the incompressible material which is used in conby a mixture of waterand cement as the incompressible material.

The invention will be better understood by reference to the accompanyingdrawing wherein similar figures denote similar parts throughout, and inwhich:

Figure l is a diagrammatic cross-sectional view cut through the centerof the underground cavern, mine shaft and the tunnel connecting thecavern to the mine shaft;

Figure 2 is an expanded cross-sectional detail View of the sealstructure of this invention;

Figure 3 is a front view of the seal structure looking down the tunnelfrom the mine shaft prior to installation of the tile.

Referring now to Figure 1, the construction of the underground cavernwill first be described. Ordinarily, the first step in the constructionis to drill a hole to the desired depth of the proposed cavern floor.This hole may be formed in the preliminary coring operation.

The next step in the construction of the cavern is the excavation of amine shaft 13. The mine shaft may be.

provided for part or all of its length with a suitable casing 14 such asa concrete wall, if necessary. A tunnel 15 is then excavatedperpendicularly to the mine shaft 13. Depending upon the number ofcaverns desired, one or more tunnels such as 15 may be connected to thesame mine shaft. When the approximate area is reached by the tunnel 15where it is desired to construct the cavern, the main excavation takesplace and the cavern 16 is constructed. The diggings from the cavern Hare removed through the tunnel 15 and the mine shaft 13. The excavationis accomplished by the usual mining techniques.

The cavern 16 may take various shapes insofar as the profile of its wallstructure is concerned, depending upon the nature of the formation ofthe stratum and giving due consideration to the most economical methodof excavation. For example, if the substance of the cavern walls has notendency to slough or cave in, the walls may be substantially verticalas shown by the profile of Figure 1. On the other hand, in a stratum ofdense shale or silty grey shale where there is a likelihood ofsloughing, the cavern is excavated with sloping sides to obviate thisfault. When the cavern is complete, ap-

propriate connections between the hole 10 and the cavern 16 are made toprovide for the ingress and egress of the liquid to be stored. Thesewill include the valve means 17, a string of pipe 11 and a pump 18 whichare known in the art and are not a part of my invention. The tunnel 15connecting the cavern 16 to the mine shaft 13 must be sealed to preventthe escape of the stored liquid or gas from the cavern 1'6.

The seal structure A of this invention is shown on Figure 1 incross-section but the manner of construction of the seal structure canbe better understood by reference to the expanded view shown in Figure 2and referred to now.

The first step in constructing the seal structure A of this invention isto excavate a recess 19 in the wall of the tunnel 15. This excavationcan be conveniently accomplished by means of hand operated pneumaticrock chisels and drills. When the excavation of the recess 19 iscompleted, the surface of the recess may desirably be coated with asealing compound to seal any voids or crevices therein. As a sealingcompound, it may be desirable to employ a compound which is imperviousto the material to be stored in the cavern. In some instances it mayalso be desirable to support the roof of the recess 19 by means of roofsupport jacks (not shown). All surfaces of the recess 19 which are to bein contact with metal should be made as smooth as possible.

Before proceeding with the construction of the seal structure, a bolt 24should be set intothe roof of the tunnellS a short distance from thecavern facelof the recess 19. A ring and chain 25 are welded to the bolt24 for a purpose which will be described hereinafter.

The next step in the construction of the seal structure is to constructa plate 20 adjacent to the wall 19a of the recess 19. This plate 20 isdesirably constructed from a number of pre-formed sections which areassembled in situ by a seal welding or other suitable means. Thethickness of the plate 20 need not be great and in the present instancea thickness of A was found to be suitable. For the purpose of providingstructural support, stifieners such as angle bars 22 may be welded tothe plate 20. Plate 20 is held against the wall 19a by means of theexpansion bolts 21. Void spaces between the recess wall 19a and theplate 20 may be filled with cement or other sealing material.

In order to complete the cavern side bulk head, a plate 23 isconstructed adjacent recess Wall 19b. This plate is similar to the plate20 and is constructed in a like manner. Expansion bolts 21 hold theplate adjacent to the wall 1%. When plate 23 is finally assembled, anumber of reinforcing spacer rods 26 are welded to the plates 20 and 23.A cement fill pipe 27 and an air vent pipe 28 are then installedcommunicating with the area between plates 23 and 20. A conduit 29 whichwill be used as a manway is then welded to the plates 23 and 20 in anarea provided in the plates 20 and 23 at the time ofconstruction. Thesection 29 has a flange 30 on the cavern side.

The area 31 between the plates 20 and 23 is filled with anincompressible material such as cement through the fill pipe 27. Ifcement is employed to fill the space 31, the high heat of hydration ofcement may render it impractical to completely fill the space 31 in asingle dump. If such is the case, several dumps can be spaced atsuitable intervals. The last dump should be continued until materialbegins to come out through the vent pipe 28.

The next step in the construction of the seal involves the centersection. I beams 32 are placed on the floor of the recess 19 and thesebeams support a center cylinder form 33. The center cylinder form 33 isassembled by welding or other suitable means from a number of pre-formedsections. The center cylinder form 33 should preferably be as nearlycircular as is practicable, but it is not necessary that it 'beperfectly circular.

When the center cylinder form 33 has been assembled and has been weldedto the plate 23, the shaft end form plate 34 is constructed in the samemanner as plates 20 and 23 but several sections of this plate are leftout for later insertion for reasons that will become apparenthereinafter. The plate 34 is held against the recess wall 19d by theexpansion bolts 21. Plate 34 has stiffeners 22 welded to its face.

The conduit section 35 is installed and welded to conduit section 29 andplate 34. Conduit section 35 has a flange 36 at its shaft end.Stiffeners 37 may be welded to the top side of the conduit section 35and to the roof of the center cylinder form 33.

Ring form 38 is assembled adjacent to the wall 190. This form isconstructed in a manner similar to that employed in the construction ofplate 34 and is held in place by means of the expansion bolts 21. Thering form 38 is Welded to the outer edge of the center cylinder form 33.

The fill pipe 39 and the vent pipes 40 and 41 are now installed. Ventpipe 44 is installed in the squeeze void 43 and a fill pipe 45 is alsoinstalled to service the void 43. The remaining sections of plate 34 arenow installed. Concrete or like material may now be dumped into the voldspace 42 Within the center cylinder form 33 through the fill pipe 39.Once again, because of the heat of hydration of such materials, it willprobably be necessary to fill the space 42 by dumping the concrete orlike material in small amounts at suitable intervals.

When the center void space 42 is completely filled with concrete, asuitable interval for the complete setting. of

this material should be allowed. When this interval has elapsed, thevoid space 43 should be filled and maintained under a high pressure witha cement which is impervious to the material to be stored and which iscapable of forming a tight bond with the surrounding stratum. The cementshould preferably contain an additive, many of which are known to theart, which will prevent its shrinkage upon setting. The filling isaccomplished by pumping a mixture of this cement under a high pressurethrough the fill line 45. The pumping is continued until the specialcement begins to discharge through the vent line 44. When the cementbegins to flow out of the vent line 44, the valve 46 should be closedand pumping continued until the pressure within the squeeze void 43 isat least 300 lbs. per square inch and preferably somewhat higher. Whenthis pressure is attained, the valve 47 in the fill line isclosed.

As the last step in completing the construction of the seal, the cavernside manway blind flange 48 is secured to the flange 30 by rneansofbolts 49. In order to hold the blind flange 43 in position whilesecuring it to the flange 30, it will be necessary to employ the chain25 heretofore mentioned by securing it to the flange 48. The seal iscompleted by installation of the shaft side manway blind flange 50 whichis secured to the flange 36 by means of bolts 49. The blind flanges 48and 50 are sealed by appropriate gaskets (not shown).

When the seal has been completed, a tile or pipe 51 is laid from theshaft side of the sealed structure part way' up the shaft 13. .The area52 around the tile 51 is filled to a level above the highest pointwithin the cavern with concrete or a mixture of crushed rock andconcrete so that the seal structure will. be subjected to a compressivestress. As a final precaution, the area 53 shown on Figure 1 within thetile may be filled with water.

Figure 3 of the patent drawing shows the various parts of the sealedstructure looking from the shaft 13 towards the cavern 16. The importantfeature to be noted in this figure is that all of the main structuralelements of the seal structure have a diameter larger than the diameterof the tunnel 15. It is this feature of the seal structure which makesit particularly useful as the stress imposed on the surrounding stratumis largely compressive in nature rather than shearing.

It will be obvious to those skilled in the art that modifications of theparticular sealing means disclosed may be made. modifications of theinvention as would reasonably fall within the scope of the appendedclaims.

I claim:

1. In combination with an underground storage cavern, a passagecommunicating with the cavern having a pair of spaced-part lateralenlargements in the wall thereof forming continuous trenches ofappreciable depth and limited axial extent in the material bounding thepassage, the side walls of said trenches being substantially normal tothe axis of the passage and the extent of the latter between thetrenches also beingenlarged with respect to the normal cross-section ofthe passage but to.a lesser However, it is intended to cover all suchextent than the trenches, a pair of metal bulkheads of considerablylarger area than the passage disposed in one of said trenches with theirperipheral portions respectively against the side walls of said onetrench, whereby said bulkheads extend in substantially parallel axiallyspaced relation transversely of the passage and substantially into theboundary material beyond the wall of the passage, a first mass ofsubstantially incompressible set material completely filling said onetrench between the peripheral portions of the bulkheads therein andagainst the bottom of the trench, said first mass further extendinginwardly between the bulkheads well beyond the thus embedded peripheralportions of the same, a second mass of substantially incompressiblematerial extending along the wall of the passage between the twotrenches and filling the other of said trenches, the second mass alsoextending inwardly over the length thereof well beyond the portionsthereof embedded in the boundary material between the trenches and insaid other trench, said pair of metal bulkheads. and first and secondmasses of substantially incompressible material together forming anembedded seal structure of general spool shape in the passage, andsealing compound disposed under substantial pressure between the outerperiphery of the intermediate portion of said structure, between therelatively enlarged ends thereof defined by the trenches, and theboundary material surrounding said intermediate portion to form a tightbond therewith.

2. The combination set forth in claim 1 wherein the intermediate portionof the seal structure between the enlarged ends thereof is enclosed by acontinuous metal liner, and the sealing compound under pressure isbetween said liner and the surrounding boundary material.

3. The combination set forth in claim 2 wherein one end of said liner isdisposed against the inboard bulkhead of the pair of the same in saidone trench, the other end of the liner is approximately in the plane ofthe inboard side wall of said other trench, a metal flange sectionextends outwardly from about said other end of the liner into said othertrench against the inboard side wall thereof, and a further metalbulkhead of considerably larger area than the cross-section of thetunnel is disposed in the other trench against the outboard side wall ofthe same, that portion of the second incompressible mass filling saidother trench being between said metal flange section and furtherbulkhead therein.

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